The following plugins do not display a description when you select the plugin row (in latest nightly dev build from Nov 2016):
Classic Disc Numbers
Copy Cluster to Clipboard
Feat. Artist in Titles
Feat. Artists Removed
When you select these plugins, the previously selected plugin remains displayed - the description area is not blanked out. There are no errors in the Debug/Error log.
I suspect that this is a combination of:
a. Metadata missing from the start of the plugins; and
b. Failure of Picard code to handle missing metadata is a nice fashion.